1. Field of the Invention
The present invention relates to testing devices, and particularly to a stress corrosion cracking testing device that is capable of testing engineering materials, particularly normally ductile and brittle metals for failure due to stress corrosion cracking (SCC) at high temperature and high pressure.
2. Description of the Related Art
Stress corrosion cracking refers to the sudden failure of structural materials, such as normally ductile and brittle metals and metal alloys, under conditions in which the structural material is subject to tensile stress in a corrosive environment. Stress corrosion cracking (SCC) is considered to be one of the most dangerous forms of failure due to the typical locations at which such failures can occur and the potentially devastating impact therefrom. SCC of in-service components can occur in areas that are undetectable and difficult to access. Due to the inconspicuous nature of these occurrences, sudden failure of the component(s) is often accompanied by catastrophic results. In order to counter such potential dangers, a complete shutdown may be necessary for maintenance and repair. Such actions can incur prohibitive costs, both from loss of production and the maintenance that may be required.
Due to the above, engineers and designers must carefully assess various different materials to be used in making the components for an industrial environment. At the very least, it is importance to accurately determine the stress intensity factor (KI) and the threshold stress intensity (KIsec) in the components made from those materials in order to determine the life expectancy of the component in corrosive environments, conformance to construction standards, and the ability of the component to meet performance demands.
Various different techniques and testing apparatus/rigs have been developed to address this issue. A typical testing unit involves the use of a specimen placed in a rig and exposed to tensile stress. Measurements are taken to determine KI and KIsec. However, the inventors are not aware of any testing devices that assess SCC at extreme conditions, such as at very high pressures and temperatures actually experienced by components in an industrial setting. Moreover, the majority of these testing rigs tend to be bulky, requiring relatively large amounts of space, and the testing rigs are expensive, both in terms of the device itself and the necessary upkeep and specialty needs. In addition, the conventional fracture specimens used for testing, such as compact tension (CT) and pre-cracked double cantilever beam (DCB) specimens, are relatively expensive and bulky, requiring a rather large thickness in order to achieve plane strain conditions. In some situations, those types of specimens cannot be obtained from failed components.
In light of the above, it would be a benefit in the art of materials testing to provide a testing device that is relatively inexpensive and compact and can provide SCC performance data for materials that will be exposed to extreme or high temperatures, high pressures, and corrosion. Thus, a stress corrosion cracking testing device solving the aforementioned problems is desired.